FIGS. 1, 2a, 2b and 2c show specific embodiments of understood valve-seat members. FIGS. 2a, 2b and 2c show schematic representations of three typical basic constructions of valve-seat members having injection openings. While in the case of the configuration approach according to FIG. 2c, the valve-seat member having a flat and even end face closes the downstream valve end of the fuel injector toward the combustion chamber, in the case of the likewise configuration approaches according to FIGS. 2a and 2b, the valve-seat members are formed with a center area of the valve-seat member that projects outwardly in dome-like manner in the injection direction and includes the injection openings. The dome is either a tapered dome having a conical lateral surface in the center area (e.g., DE 10 2013 219 027 A1) or a rounded dome having a curvature running outwardly in convex, spherical manner (e.g., EP 2 333 306 A1). In both cases, the dome-like center area of the valve-seat member changes over smoothly and steadily into a flat and even end face of the valve-seat member.
In the case of such valve-seat members, the entire dome area is an area critical in terms of strength. It is stressed by the valve needle pounding it millions of times with its valve-closing member. In addition, the system pressure of the fuel acts on the entire inner side of the dome-like center area. These stresses, accompanied by the risk of a deformation of the dome area with negative influence on the quality of the valve-seat face, have an effect on the tightness demands and the endurance strength of the valve-seat member in this area.